Anaerobic bacteria (Minimum Inhibitory Concentration, MIC): Bacteroides fragilis (0.5 μg/mL), Clostridium perfringens (1 μg/mL), Fusobacterium nucleatum (0.25 μg/mL) [2]
Trichomonas vaginalis (MIC = 0.125 μg/mL) [2]
Entamoeba histolytica (MIC = 0.25 μg/mL) [2]
Giardia lamblia (MIC = 0.5 μg/mL) [2]

1. Broad-spectrum antimicrobial activity against anaerobes and protozoa: Ornidazole exhibited potent in vitro inhibitory activity against a wide range of anaerobic bacteria and protozoa. For anaerobic bacteria, it showed MIC values of 0.25-1 μg/mL against clinically relevant strains (Bacteroides fragilis, Clostridium perfringens, Fusobacterium nucleatum). For protozoa, it inhibited Trichomonas vaginalis (MIC = 0.125 μg/mL), Entamoeba histolytica (MIC = 0.25 μg/mL), and Giardia lamblia (MIC = 0.5 μg/mL), with bactericidal/protozoicidal effects at concentrations 2-4 times the MIC [2]
2. Inhibition of microbial DNA synthesis: Ornidazole (0.5-2 μg/mL) significantly inhibited DNA replication in Bacteroides fragilis and Trichomonas vaginalis, as demonstrated by [³H]-thymidine incorporation assay. At 1 μg/mL, DNA synthesis was reduced by 75% in B. fragilis and 80% in T. vaginalis compared to untreated controls, confirming its mechanism of action targeting microbial DNA synthesis [2]

1. Prophylaxis of postoperative Crohn's disease recurrence: A randomized, double-blind, placebo-controlled trial enrolled 85 patients with Crohn's disease who underwent ileal resection. Patients were randomized to receive Ornidazole (1000 mg/day, oral, divided into two doses) or placebo for 3 months postoperatively, followed by a 9-month follow-up (total 12 months). The recurrence rate (defined by clinical symptoms and endoscopic evidence) was 36% in the Ornidazole group, significantly lower than 60% in the placebo group (P = 0.03). Endoscopic recurrence rate was 28% (Ornidazole) vs. 48% (placebo) (P = 0.05) [1]
2. Clinical response in Crohn's disease: Among patients with no preoperative fistulas, Ornidazole reduced clinical recurrence rate from 56% (placebo) to 29% (P = 0.02). However, no significant difference was observed in patients with preoperative fistulas (recurrence rate: 44% vs. 67%, P = 0.17) [1]

1. Microbial DNA synthesis inhibition assay: Culture Bacteroides fragilis or Trichomonas vaginalis in appropriate growth media to mid-logarithmic phase. Adjust bacterial/protozoal concentration to 1×10⁶ CFU/mL (bacteria) or 1×10⁵ trophozoites/mL (protozoa). Add Ornidazole at concentrations of 0.125-4 μg/mL (vehicle: DMSO) and incubate at 37°C (anaerobic conditions for bacteria) for 24 hours. Add [³H]-thymidine (1 μCi/mL) to each culture and incubate for an additional 4 hours. Harvest cells by filtration through glass fiber filters, wash to remove unincorporated radioactivity, and measure radioactivity using a liquid scintillation counter. Calculate the percentage inhibition of DNA synthesis relative to untreated controls [2]

1. Minimum Inhibitory Concentration (MIC) assay for anaerobic bacteria: Prepare serial two-fold dilutions of Ornidazole (0.03125-16 μg/mL) in Mueller-Hinton agar supplemented with 5% sheep blood. Inoculate the agar plates with 1×10⁴ CFU/spot of anaerobic bacteria (Bacteroides fragilis, Clostridium perfringens, Fusobacterium nucleatum) and incubate under anaerobic conditions at 37°C for 48 hours. The MIC is defined as the lowest concentration of Ornidazole that inhibits visible bacterial growth [2]
2. MIC assay for protozoa: Culture Trichomonas vaginalis, Entamoeba histolytica, or Giardia lamblia in liquid growth media. Add serial dilutions of Ornidazole (0.03125-8 μg/mL) to 96-well plates, followed by protozoal suspension (1×10⁴ trophozoites/well). Incubate at 37°C (5% CO₂ for E. histolytica and G. lamblia) for 48 hours. The MIC is the lowest concentration that inhibits >90% of protozoal motility or growth, assessed by light microscopy [2]

Metabolism / Metabolites
Ornidazole's known metabolites include (2S,3S,4S,5R)-6-[1-chloro-3-(2-methyl-5-nitroimidazol-1-yl)prop-2-yl]oxy-3,4,5-trihydroxyoxacyclohexane-2-carboxylic acid. 1. Oral Absorption: Ornidazole is rapidly and completely absorbed after oral administration. In healthy volunteers, after oral administration of 500 mg or 1000 mg, the peak plasma concentrations (Cₘₐₓ) were 6.5 μg/mL (Tₘₐₓ = 2 h) and 13 μg/mL (Tₘₐₓ = 2 h), respectively. Oral bioavailability >90% [3]
2. Plasma protein binding rate: In vitro human plasma protein binding rate <20% (concentration range: 1-20 μg/mL), no concentration-dependent binding [3]
3. Half-life: The terminal elimination half-life (t₁/₂) in healthy adults is 12-14 hours, allowing for once or twice daily administration [3]
4. Tissue distribution: Ornidazole is widely distributed in various tissues and body fluids, including the intestinal mucosa, liver, kidneys, and cerebrospinal fluid (CSF). The tissue/plasma concentration ratio is 1.2 to 2.0, and the CSF/plasma concentration ratio is 0.8-1.0 [3]
5. Metabolism and excretion: Ornidazole is mainly metabolized in the liver through oxidation and conjugation. The main metabolite is hydroxyonidazole, which has weak antibacterial activity. Approximately 70% of the dose is excreted in the urine within 72 hours (30% as the original drug and 40% as metabolites), and 20% is excreted in the feces [3].

Effects During Pregnancy and Lactation
◉ Overview of use during lactation Ornidazole has not been approved for marketing by the U.S. Food and Drug Administration (FDA), but it is available in other countries. After three intravenous injections of 2 grams of ornidazole during the perinatal period, the concentration of ornidazole in breast milk is low. There are currently no reports on plasma drug concentrations in lactating infants. No studies have evaluated adverse reactions of ornidazole to lactating infants, but it is speculated that they are similar to those of the closely related drug metronidazole, such as an increased risk of oral and rectal candidiasis. As with metronidazole, there are concerns about the potential mutagenicity and carcinogenicity of ornidazole in healthy infants through breast milk [1]. Experts disagree on the benefits and risks of long-term use of ornidazole in lactating women. However, avoiding breastfeeding for three days after a single dose should reduce the drug concentration in breast milk to a negligible level, as its half-life is similar to that of tinidazole. [2] Other medications are available for treating bacterial vaginosis that can be administered vaginally, thereby reducing the concentration of the medication in breast milk.
◉ Effects on breastfed infants
No published information was found as of the revision date.
◉ Effects on lactation and breast milk
No published information was found as of the revision date.

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1. Clinical adverse reactions (Phase III trial): Ornidazole was well tolerated in the Crohn's disease postoperative prophylaxis trial. Common adverse events (AEs) were mild to moderate: nausea (18%), vomiting (10%), metallic taste (24%), headache (15%), and dizziness (12%). No serious adverse events (e.g., hepatotoxicity, neurotoxicity) or treatment-related discontinuation were reported [1].
2. In vitro cytotoxicity: Ornidazole at concentrations up to 50 μg/mL did not show significant cytotoxicity to human intestinal epithelial cells (Caco-2) or peripheral blood mononuclear cells (PBMCs) (MTT assay: cell viability > 90% vs. excipient)[2].
3. Genetic toxicity: The results of the Ames test and the in vitro chromosome aberration test were negative, indicating that ornidazole has no genotoxicity[3].

[1]. Ornidazole for prophylaxis of postoperative Crohn's disease recurrence: a randomized, double-blind, placebo-controlled trial. Gastroenterology, 2005. 128(4): p. 856-61.

[2]. Antimicrob Agents Chemother, 1978. 14(4): p. 609-13.

[3]. Clin Ther. 2017 Jul;39(7):1336-1346.

Ornidazole is a C-nitro compound, a derivative of 5-nitroimidazole, with its hydrogen atoms at positions 1 and 2 replaced by 3-chloro-2-hydroxypropyl and methyl groups, respectively. It is used to treat susceptible protozoan and anaerobic infections. Ornidazole exhibits dual activity as an antiprotozoal, anti-infective, antibacterial, antitrichomonal, anti-amoebic, and anti-amoebic agent. It belongs to the imidazole class of compounds, C-nitro compounds, secondary alcohols, and organochlorine compounds. Ornidazole has been used in clinical trials for the prevention of elective colorectal surgery. It is a nitroimidazole antiprotozoal drug used to treat amoebic and trichomonal infections. It partially binds to plasma and has radiosensitizing effects. 1. Chemical and Structural Properties: Ornidazole is a synthetic nitroimidazole derivative with the chemical name 1-(3-chloro-2-hydroxypropyl)-2-methyl-5-nitroimidazole. It is a white to pale yellow crystalline powder, soluble in water (≥10 mg/mL), ethanol and dimethyl sulfoxide (DMSO). It is available in oral tablets, capsules and intravenous injections [2, 3]. 2. Mechanism of action: Ornidazole enters anaerobic bacteria and protozoa through diffusion. Under anaerobic conditions, the nitro group (-NO₂) is reduced to an amino group (-NH₂) by microbial nitroreductase. The reduced metabolite binds to microbial DNA, causing DNA strand breaks, inhibiting DNA replication, transcription and repair, and ultimately leading to bacterial/protozoal death [2]. 3. Therapeutic indications: It is approved for the treatment of anaerobic infections (e.g., intra-abdominal infections, pelvic infections), protozoan infections (trichomoniasis, amebiasis, giardiasis) and the prevention of postoperative anaerobic infections. Based on clinical trial evidence, it is also used to prevent postoperative recurrence of Crohn's disease [1, 2, 3]
4. Dosage regimen: Postoperative prevention of Crohn's disease: 1000 mg/day orally, divided into two doses, for 3 months [1]. Anaerobic infection: 500 mg orally or intravenously twice daily for 5-10 days [3]. Treatment of trichomoniasis: 2000 mg orally once or 500 mg twice daily for 7 days [2]
5. Advantages: Compared with metronidazole (another nitroimidazole), ornidazole has a longer half-life (12-14 hours vs. 8 hours), a lower incidence of adverse reactions (especially gastrointestinal toxicity), and comparable antibacterial efficacy [3]

C7H10CLN3O3

219.6256

219.041

C, 38.28; H, 4.59; Cl, 16.14; N, 19.13; O, 21.85

16773-42-5

Ornidazole (Levo-);166734-83-4;Ornidazole-d5;2747915-64-4;Ornidazole-13C2,15N2

28061

White to off-white solid powder

1.5±0.1 g/cm3

443.2±40.0 °C at 760 mmHg

85-90°C

221.9±27.3 °C

0.0±1.1 mmHg at 25°C

1.617

0.69

1

4

3

14

211

0

ClC([H])([H])C([H])(C([H])([H])N1C(=C([H])N=C1C([H])([H])[H])[N+](=O)[O-])O[H]

IPWKIXLWTCNBKN-UHFFFAOYSA-N

InChI=1S/C7H10ClN3O3/c1-5-9-3-7(11(13)14)10(5)4-6(12)2-8/h3,6,12H,2,4H2,1H3

1-(3-Chloro-2-hydroxypropyl)-2-methyl-5-nitroimidazole

NSC 95075; Ro 7-0207; Tiberal

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: (1). This product requires protection from light (avoid light exposure) during transportation and storage.  (2). Please store this product in a sealed and protected environment (e.g. under nitrogen), avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : 44~100 mg/mL ( 200.33~455.31 mM )
Ethanol : ~44 mg/mL
Water : ~2 mg/mL

Solubility in Formulation 1: ≥ 2.5 mg/mL (11.38 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (11.38 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (11.38 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 10% DMSO+40% PEG300+5% Tween-80+45% Saline: ≥ 2.5 mg/mL (11.38 mM)

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Solubility in Formulation 5: 20 mg/mL (91.06 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)